The scaphotrapeziotrapezoid (STT) joint is one of the key link joints between the proximal and the distal carpal rows. We assessed the relationship between the scaphotrapezium (STm) andscaphotrapezoid (STd) joints using computerised tomographyand hypothesised the ratio of STm is =/< STd joint due to which, the possibility of failure of trapeziectomy due to metacarpal collapse is insignificant. We reviewed CT scans of wrist joints of 113 eligible patientsfrom our wrist database between 2009 and 2014 for our study. 31 patients were randomised for interobserver correlation. Reformatted multi-planar sequences were analysed. The ratio of theSTm: STdin sagittal and coronal measurementswas evaluated. Interobserver variations were assessed using the Pearson coefficient.

The sex distribution included 68 males and 29 females, 49 left and 64 right wrists. The STm area was larger in 86 (76%) as compared to STd in 27(24%). Average trapezium to trapezoid ratio was 1:1.5. Ratio of area of trapezium: trapezoid joint is 0.30. The anatomic ratio of the STm in the coronal and sagittal planesis 0.3 and that of the STd joint is 0.2. Ratio of the STm: STd in the coronal plane is 0.29. Pearson's coefficient > 0.8.

A small subset of patients undergoing trapeziectomy alonefor stage II- IV carpometacarpal arthritis of the thumb are at risk of impingement of the first metacarpal due to collapse. Our assessment of the anatomical relationship of the STT joint with CT scan proves that although the area the STm joint is generally larger than the STd joint, there is no significant correlation on the whole.